Elevator motor drive tolerant of an irregular power source

Abstract

A hoist motor ( 12 ) for an elevator ( 14 ) is continuously driven from an irregular power supply ( 16 ). A regenerative drive ( 10 ) delivers power between the power supply ( 16 ) and the hoist motor ( 12 ). A controller ( 11 ) measures a power supply voltage in response to a detected change in the power supply voltage and controls the regenerative drive ( 10 ) to adjust a nominal motion profile of the elevator ( 14 ) in proportion with an adjustment ratio of the measured power supply voltage to a normal power supply voltage.

The invention claimed is: 
     
       1. A system for continuously driving a hoist motor for an elevator from an irregular power supply, the system comprising:
 a regenerative drive for delivering power between the power supply and the hoist motor; and 
 a controller operable to measure a power supply voltage in response to a detected change in the power supply voltage and to control the regenerative drive to adjust a nominal motion profile of the elevator in proportion with an adjustment ratio of the measured power supply voltage to a normal power supply voltage. 
 
     
     
       2. The system of  claim 1 , wherein the nominal motion profile comprises at least one of maximum acceleration, maximum steady state speed, and maximum deceleration of the elevator when the power supply voltage is normal. 
     
     
       3. The system of  claim 2 , and further comprising:
 a sensing device for determining whether the hoist motor is motoring or generating, wherein the controller further operates the regenerative drive to adjust the motion profile of the elevator in proportion with the adjustment ratio based on whether the hoist motor is motoring or generating. 
 
     
     
       4. The system of  claim 3 , wherein the maximum acceleration and maximum steady state speed are adjusted proportionally with the adjustment ratio when the elevator is motoring, wherein the maximum deceleration and maximum steady state speed are adjusted proportionally with the adjustment ratio when the elevator is generating, and wherein the motion profile is not adjusted when the elevator is neither motoring nor generating. 
     
     
       5. The system of  claim 1 , wherein the regenerative drive comprises:
 a converter to convert alternating current (AC) power from the power supply into direct current (DC) power; 
 an inverter to drive the hoist motor by converting the DC power from the converter into AC power and, when the hoist motor is generating, to convert AC power produced by the hoist motor to DC power; and 
 a power bus connected between the converter and the inverter to receive DC power from the converter and the inverter. 
 
     
     
       6. The system of  claim 5 , wherein the controller controls the inverter to drive the hoist motor based on the adjusted nominal motion profile of the elevator. 
     
     
       7. The system of  claim 5 , wherein the controller further adjusts the voltage across the power bus proportionally with the adjustment ratio in response to a change in the power supply voltage. 
     
     
       8. The system of  claim 1 , and further comprising:
 line reactors connected between the regenerative drive to the power supply. 
 
     
     
       9. The system of  claim 8 , and further comprising:
 a thermal control module for operating a drive cooling fan at maximum speed when the current through the line reactors approaches a continuous current rating of the line reactors. 
 
     
     
       10. A method for continuously driving a hoist motor for an elevator from an irregular power supply comprising:
 measuring a power supply voltage in response to a change in the power supply voltage; 
 adjusting a nominal motion profile of the elevator in proportion with an adjustment ratio of the measured power supply voltage to a normal power supply voltage to produce a new motion profile, wherein the nominal motion profile comprises at least one of maximum acceleration, maximum steady state speed, and maximum deceleration of the elevator when the power supply voltage is normal; and 
 driving the elevator hoist motor with a drive current based on the new motion profile. 
 
     
     
       11. The method of  claim 10 , wherein adjusting a nominal profile of the elevator comprises determining whether the hoist motor is motoring or generating and adjusting the motion profile of the elevator in proportion with the adjustment ratio based on whether the hoist motor is motoring or generating. 
     
     
       12. The method of  claim 11 , wherein the maximum acceleration and maximum steady state speed are adjusted proportionally with the adjustment ratio when the elevator is motoring, wherein the maximum deceleration and maximum steady state speed are adjusted proportionally with the adjustment ratio when the elevator is generating, and wherein the motion profile is not adjusted when the elevator is neither motoring nor generating. 
     
     
       13. The method of  claim 12 , and further comprising:
 driving the elevator hoist motor with a drive current based on the nominal motion profile when the power supply returns to a normal power supply voltage. 
 
     
     
       14. A system for controlling a regenerative drive including a converter and inverter connected by a direct current (DC) bus, the inverter connected to an elevator hoist motor and the inverter connected to an alternating current (AC) power supply via line reactors, the system comprising:
 a voltage sensor for detecting a change in a power supply voltage and measuring the power supply voltage; 
 an elevator motion profile generator which, in response to a change in the power supply voltage, generates a new motion profile that is a nominal motion profile proportionally adjusted by an adjustment ratio of the measured power supply voltage to a normal power supply voltage; 
 an error correction device that receives the new motion profile and actual operating parameters of the hoist motor and produces an error signal related to a difference between the actual operating parameters and target operating parameters based on the new motion profile; and 
 an inverter controller that receives the error signal and controls the inverter to drive the hoist motor to the target operating parameters. 
 
     
     
       15. The system of  claim 14 , wherein the nominal motion profile comprises at least one of maximum acceleration, maximum steady state speed, and maximum deceleration of the elevator when the power supply voltage is normal. 
     
     
       16. The system of  claim 15 , wherein the elevator motion profile generator adjusts the maximum acceleration and maximum steady state speed proportionally with the adjustment ratio when the elevator is motoring, wherein the elevator motion profile generator adjusts the maximum deceleration and maximum steady state speed proportionally with the adjustment ratio when the elevator is generating, and wherein the elevator motion profile generator does not adjust the motion profile when the elevator is neither motoring nor generating. 
     
     
       17. The system of  claim 14 , and further comprising:
 a DC bus voltage regulator operable to adjust a voltage across the DC bus proportionally with the adjustment ratio in response to a change in the power supply voltage. 
 
     
     
       18. The system of  claim 14 , and further comprising:
 a current regulator for determining a difference between the power supply voltage and a DC bus voltage and operating the converter to balance the power supply voltage and the DC bus voltage to regulate the current across the line reactors. 
 
     
     
       19. The system of  claim 18 , wherein the converter comprises a plurality of power transistor circuits, each power transistor circuit comprising a transistor and a diode connected in parallel, and wherein the current regulator employs pulse width modulation to produce gating pulses that periodically switch the transistors to balance the power supply voltage and the DC bus voltage. 
     
     
       20. The system of  claim 14 , wherein the inverter comprises a plurality of power transistor circuits, each power transistor circuit comprising a transistor and a diode connected in parallel, and wherein the inverter controller employs pulse width modulation to produce gating pulses to periodically switch the transistors to drive the hoist motor to the target operating parameters.